In a known pneumatic pump for use in intermittent compression therapy a number of outlet sockets are provided for attachment of supply hoses. When a supply hose is disconnected from an outlet socket during operation of the pump it is necessary to seal the socket in order to maintain the efficiency of air supply to other outlet sockets. Sealing in the known construction is achieved by a simple plug or cap which is inserted into or over the outlet socket to stop egress of air.